The present invention is directed to magnetic thin film head (TFH) devices for recording magnetic transitions on a moving magnetic medium and, more particularly, to a magnetic head that reduces transition curvature for very narrow writer widths.
In the operation of a typical inductive TFH device, a moving magnetic storage medium is placed near the exposed pole-tips of the TFH device. TFH is composed of the magnetic poles and coils wrapping around the poles. During a write operation, a current flowing through the coils induces magnetic flux in the magnetic poles and generates the magnetic field across the gap between pole tips, so called writer gap. This field extends (i.e. is fringing) into the nearby moving storage medium, inducing or writing a magnetic domain in the medium. The part of fringe field extending not through the writer gap but from the side of the top pole to the bottom pole can erase edges of the neighboring written tracks and therefore negatively affect the quality of written tracks. Alternating current causes writing magnetic domains of alternating polarity in the storage medium.
With ever increasing area densities there is a need for a head producing a very narrow track width and a very small bit cells down the track direction. The top pole width defines the width of the track and the writer gap length determines the bit cell length. As tracks get narrower, a curved part of the written track becomes a larger portion of the written track and is determined largely by the shape of the pole tip, magnetic properties of the material used at the writer gap length and write current. A fringe field extends into the nearby moving magnetic storage medium, inducing (or writing) a magnetic domain (in the medium) in the same direction. Impressing current pulses of alternative polarity across the coil causes the writing of magnetic domains of alternating polarity in the storage medium.
Prior-art magnetic recording inductive TFH devices include top and bottom magnetic core pole layers, usually of the alloy Nixe2x80x94Fe (permalloy), connected through a via in the back-portion area, and separated by a thin gap layer between the pole-tips in the front of the device. The bottom pole-tip is usually designed to be wider than the top pole-tip in order to prevent xe2x80x9cwraparoundxe2x80x9d due to misregistration or misalignent, as taught by R. E. Jones in U.S. Pat. No. 4,219,855. Alternatively, one or both pole-tips are trimmed by ion-milling or by reactive ion etching (RIE) to ensure similar width and proper alignment. Such a technique is disclosed, for example, by Cohen et al. in U.S. Pat. No. 5,141,623. As the track width decreases in order to increase the recording density, the write head pole-tips must be very narrow. P. K. Wang et al. describe elaborate schemes to obtain pole-tips for writing very narrow track width, in IEEE Transactions on Magnetics, Vol. 27, No. 6, p. 4710-4712. November 1991.
One of the problems associated with the prior-art pole-tip designs is that during write operations, substantial noise is introduced along the track-edges (on the magnetic storage medium), which adds to the noise generated by the medium during read operations. During the write operations, significant portions of the intense magnetic flux lines, emanating from the corners and side-edges of the pole-tips, deviate from a direction parallel to the track""s length. The non-parallel magnetic field magnetizes the medium in the wrong directions, giving rise to noise along the track-edges. This noise is usually characterized as xe2x80x9ctrack-edge fringing noisexe2x80x9d and is a major obstacle to increasing the track density. According to a paper by J. L. Su and K. Ju in IEEE Transactions on Magnetics, Vol. 25, No. 5, pp. 3384-3386, September 1989, the track-edge noise in this particular case extends about 2.5 xcexcm on each side of the written track. The high track-edge noise and wide writer width produced by the conventional design, limits its usefulness to relatively low track densities. As track density increases, the track width decreases, but the percentage of the curved transition relative to the track width increases.
U.S. Pat. No. 5,673,163 (Cohen) discloses a pinched-gap magnetic recording thin film head where substantial contact is established between the bottom pole-tip 14 and top pole-tip 18 thereby pinching or confining a gap segment 16. In a preferred embodiment the bottom pole-tip 14 and top pole-tip 18 are in actual physical contact. In other embodiments a small gap may separate the bottom and top pole-tips. The small gap or separation should be small enough to prevent the magnetic flux lines from emanating significantly from the pole-tips in those regions. The separation of the pole-tips in those regions should not exceed about 25% of G, the vertical distance between pole-tips in the gap area. Preferably, the separation should not exceed 5% of G.
According to a first aspect of the invention, there is provided a magnetic transducer device having a bottom magnetic pole, a nonmagnetic gap layer deposited on the bottom pole and a top pole deposited on the gap layer. The top magnetic pole has an upper portion and a lower portion. The lower portion faces a surface of the bottom pole and has a middle section that is separated from the bottom pole by the gap layer by a first distance. The lower portion has end portions located at each end of the middle portion that are separated from the bottom pole by the gap layer by a second distance where the second distance is greater than 25% of the first distance.
According to another aspect of the invention, the second distance ranges from about greater than 25% to about 60% of the first distance.
According to still another aspect of the invention, the device has a width measured between a left and a right side of the top pole ranging from about 0.3 microns to about 1.5 microns.